/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.util;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * Keep track of a reference count on a resource and close it when the count
 * hits zero.
 * 
 * By itself, this class could have some race conditions since there is no
 * synchronization between the refcount check and the close. Solr's use in
 * reference counting searchers is safe since the count can only hit zero if
 * it's unregistered (and hence incref() will not be called again on it).
 * 
 * @version $Id: RefCounted.java 779125 2009-05-27 11:58:18Z noble $
 */

public abstract class RefCounted<Type> {
	protected final Type resource;
	protected final AtomicInteger refcount = new AtomicInteger();

	public RefCounted(Type resource) {
		this.resource = resource;
	}

	public int getRefcount() {
		return refcount.get();
	}

	public final RefCounted<Type> incref() {
		refcount.incrementAndGet();
		return this;
	}

	public final Type get() {
		return resource;
	}

	public void decref() {
		if (refcount.decrementAndGet() == 0) {
			close();
		}
	}

	protected abstract void close();
}
